Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$213.52	7.353%	$229.2201	$229.22	$229.20	$229.20
Purchase #2	$142.75	12.740%	$160.9364	$160.94	$160.95	$160.90
Purchase #3	$131.33	10.241%	$144.7795	$144.78	$144.80	$144.80
Purchase #4	$51.37	5.373%	$54.1301	$54.13	$54.15	$54.10
Purchase #5	$100.39	8.633%	$109.0567	$109.06	$109.05	$109.10
Purchase #6	$125.31	13.667%	$142.4361	$142.44	$142.45	$142.40
Purchase #7	$128.70	11.761%	$143.8364	$143.84	$143.85	$143.80
7 purchase totals =	$893.37		$984.3953	$984.41	$984.45	$984.30